1. Field of the Invention
The present invention relates to a thermal efficiency diagnostic method and an apparatus of a combined power generation plant, which can clearly specify a thermal efficiency deterioration causative equipment (i.e. an equipment which causes a deterioration of thermal efficiency) in a case where a fluctuation or deterioration is generated in a thermal efficiency of a combined power generation plant that is already being operated and which can properly and effectively recover the thermal efficiency through inspection, repair and the like.
2. Prior Art
The thermal efficiency of a thermal power generation plant has become a focus of great attention recently in view of two points, that is, fuel saving and reduction of power generation cost. In the case where the thermal efficiency actually changes, it is imperative in the thermal efficiency management to specify which piece of equipment is responsible for the change in the thermal efficiency in a plant.
In this case, the thermal efficiency is a numerical value representing the performance of the power generation plant and expressed as a ratio of the generated electric power to a consumed fuel energy. The thermal efficiency is expressed by the following equation (1).
[Equation1]
thermal efficiency (%)=generated output (power)(W)/[fuel heat value (J/kg)xc3x97fuel consumption(kg/s)]xc3x97100xe2x80x83xe2x80x83(1)
An improvement in the thermal efficiency can lead to a reduction in the fuel consumption. In a power generation plant already existing, a performance management of the entire plant and each piece of equipment are carried out through daily checks and measurements and periodic performance tests, and afterwards, the results are reflected in plant operation and maintenance.
Among the thermal power generation plants, a combined cycle (C/C, ACC) power generation plant represents the most advanced main unit which was introduced for the first time about ten years ago. The combined cycle power generation plant has a high thermal efficiency and a high utilization factor, and in recent years, its availability has considerably increased.
However, after the combined cycle power generation plant has been in operation for about ten years elapsed, certain units begin to show noticeable deterioration in the thermal efficiency, and for this reason, it is imperative from the standpoint of economy to identify the causative equipment and pinpoint the cause of deterioration of the thermal efficiency so as to take remedial measures. In the case of discovering the cause of the deterioration of the thermal efficiency, the combined cycle power generation plant is constructed in a manner in which the gas turbine (GT) and the steam turbine (ST) exist in one unit, with these turbines are connected to one generator. For this reason, it is very difficult to determine as to whether the gas turbine or the steam turbine causes the deterioration of the thermal efficiency. In the conventional cases, although there exists a method for individually calculating each performance of the GT and ST, the above-described method is marred by the problem in its accuracy due to influence of measurement data errors as described herein later.
In the combined power generation plant, the equipment comprising the plant facility is of a large scale, and much time and labor are required for inspection, repair and so on. Moreover, the amount of equipment, time, manpower hours, cost and the like required for such work markedly increases. In the case of large-scale inspection and repair mentioned above, a good recovery result in the thermal efficiency is expected in almost all cases. Thus, in order to obtain this high recovery result, it is necessary to identify the thermal efficiency deterioration causative equipment by the thermal efficiency diagnosis for clarifying which equipment requires inspection and/or repair as compared with the conventional case. On the other hand, as stated previously herein, it is very difficult to determine which the gas turbine or the steam turbine is the cause of the deterioration. Under such circumstances, even if computer processing is introduced to perform the thermal efficiency diagnosis, the cost incurred for its facility, man/hours, management and so on are considerable, and furthermore, there remains a problem that a high diagnosis accuracy is not always obtained.
The present invention has been made taking the problem encountered in the prior art into consideration. It is, therefore, an object of the present invention to provide a thermal efficiency diagnostic method and an apparatus for a combined power generation plant capable of effectively identifying which equipment causes the deterioration in the thermal efficiency with high accuracy by accurately analyzing influences brought about by performance changes of individual equipment upon the whole plant for the purpose of properly realizing the thermal efficiency recovery through periodic inspection, repair or the like.
In the present invention, a heat balance analysis by optimum state estimation is introduced as a method of improving an accuracy of the thermal efficiency diagnosis of a combined power generation plant. In this case, the heat balance represents input and output of heat energy or electric energy of each equipment in the entire power generation plant.
The inventors of the subject application have made various studies and tests, and as a result, they have obtained the following concept. That is, a performance calculation is not independently carried out with respect to all equipment of the plant, but on the basis of each measurement data in a power generation plant, a decision was made whether optimum consistency can be made when the heat balance of the entire plant is set. It is thereby possible to make a cross check of each measurement data, thus improving the diagnosis accuracy.
More specifically, there is a dispersion of accuracy in measurement data relative to the heat input and output of each equipment of the combined power generation plant. For example, according to the conventional thermal efficiency management method of the combined cycle power generation plant, a performance calculation is carried out independently with respect to the whole of the gas turbine equipment, the whole of the exhaust gas heat steam generator (i.e. HRSG) and the whole of the steam turbine (ST). On the basis of control data measured in the power generation plant, when showing an accuracy estimation according to the conventional method of directly calculating the performance of the main equipment, the accuracy error (xcex94xcex7GT/xcex7GT) of the gas turbine efficiency is 7.8%, the accuracy error (xcex94xcex7HRSG/xcex7HRSG) of the exhaust gas heat recovery boiler efficiency is 3.2% and the accuracy error (xcex94xcex7ST/xcex7ST) of the steam turbine efficiency is 15.6%.
However, it has been found that the above-described percentages are not accurate enough to diagnose the cause with respect to the change (about 2%) in the thermal efficiency of a combined cycle power generation plant, which will usually occurs. Equations for calculating an accuracy error of the efficiency are as follows.
The accuracy of the gas turbine efficiency is obtained from the following equation (2) by differentiating and arranging both sides.
[Equation 2]
|xcex4xcex7GT/xcex7GT|=Wgas/(WLNGxe2x88x92Wgas)|xcex4Ggas/xcex4Ggas|+Wgas/(WLNGxe2x88x92Wgas)|xcex4hgas/hgas|+Wgas/WLNG|xcex4WLNG/WLNG|=7.8%xe2x80x83xe2x80x83(2)
The accuracy of the exhaust gas heat recovery boiler efficiency is obtained from the following equation (3) by differentiating and arranging both sides.
[Equation 3]
|xcex4xcex7HRSG/xcex7HRSG|=|xcex4Wwtr/Wwtr|+|xcex4Ggas/Ggas|+|xcex4hgas/hgas|=3.2%xe2x80x83xe2x80x83(3)
The accuracy of the steam turbine efficiency is obtained from the following equation (4) by differentiating and arranging both sides.
[Equation 4]
|xcex4xcex7ST/xcex7ST|=WGT/(Wtotalxe2x88x92WGT)|xcex4WGT/WGT|+|xcex4Wwtr/Wwtr|=15.6%xe2x80x83xe2x80x83(4)
Considering the above-described error propagation equation (equation (2)), it can be seen that the largest portion of the error factor of the gas turbine efficiency is based on the gas turbine exhaust gas flow rate and the gas turbine exhaust gas temperature. The influence by the gas turbine propagates to the steam turbine with an error approximately twice as the gas turbine.
In the present invention, taking the above matters into consideration, a thermal efficiency diagnosis by a heat balance analysis method incorporating optimum state estimation is employed in order to improve the accuracy in a judgment whether the gas turbine or the steam turbine is responsible for the decrease in the thermal efficiency of combined cycle power generation plant is reduced.
More specifically, by using the measurement data such as temperature, pressure, flow rate, electric power output for measurement installed in a current thermal power station, and a measurement data of a high performance torque sensor and a generator power output having a high measurement accuracy are used as a reference data so as to determine the heat balance of the plant. The standard parameter is rigid value and other parameters are adjusted so as to be consistent the standard parameters through optimum state estimation due to its high measurement accuracy.
In this case, there are key parameters which influence the results of diagnosis to a large degree and the values of key parameters are optimized within a range of the measurement accuracy. For example, the parameters include the gas turbine exhaust gas flow rate (GT exhaust gas flow rate), the gas turbine exhaust gas temperature (GT exhaust gas temperature) and the like.
Here, an optimum state estimation is carried out within a measurement accuracy range with respect to the key parameters mentioned above. The above-described optimum state estimation is to determine a state of the heat balance in which each deviation of reference parameters becomes minimum as a whole and the probability becomes maximum in the plant. A number of reference parameters are properly determined among all kinds of calculation data of the heat balance. Each reference parameter is compared with its reference value, which is the design value or the measured value for example, and each probability of parameters is calculated by taking the deviation from the reference value and the accuracy of the reference parameters into consideration. From each probability of the parameters, the entire probability that the heat balance occurs is calculated in optimum state estimation. In the case where the probability does not become maximum, adjusting the key parameter is repeated. As a function of the reference parameter for calculating the probability, for example, a normal distribution function based on the calculation/measurement accuracy each deviation or the integration of the normal distribution function is used.
The deviations of the reference parameters in the plant are as follows.
(1) Deviation of steam turbine efficiency between design value and calculation value.
The calculation value of the efficiency in the performance test of the steam turbine should not exceed the design value. Therefore, the probability function is determined so that the probability becomes high when the calculation value is less than the design value and becomes low when the calculation value is larger than the design value.
(2) Deviation of design heat transfer performance value of exhaust gas heat recovery steam generator between design value and calculation value.
The calculation value of the efficiency in a performance test of the exhaust gas heat recovery steam generator should not exceed the design value. Therefore, the probability function is determined so that the probability becomes high when the calculation value is less than the design value and becomes low when the calculation value is larger than the design value.
(3) Deviation of gas turbine efficiency between design value and calculation value.
The calculation value of the efficiency in a performance test of the gas turbine should not exceed the design value. Therefore, the probability function is determined so that the probability becomes high when the calculation value is less than the design value and becomes low low when the calculation value is larger than the design value.
(4) Deviation of exhaust gas heat recovery steam generator (HRSG) efficiency between input/output method and heat loss method.
In the HRSG efficiency, the value by the input/output heat method and the value by the loss method will naturally coincide with each other. Therefore, the probability function is determined so that the probability becomes high when they are consistent and becomes low when they are different from each other.
(5) Deviation between the calculation values (power output, temperature, etc.) and their measured values.
The values must be consistent. Therefore, the probability function is determined so that the probability becomes high when the calculation value is consistent with the measured value and becomes low when the calculation value is different from the measured value.
a) Deviation between power output values of GT and ST calculated by the input/output heat process and deviation between values measured by torque sensor, etc.
b) Deviation between an internal gas temperature of HRSG calculated by using the optimum value of GT outlet temperature and its measured value.
c) Deviation between a concentration value of exhaust gas O2 calculated using the optimum value of GT exhaust gas flow rate and its measured value.
d) Deviation between the optimum value of GT exhaust gas flow rate and its measured value.
e) Deviation between the optimum value of GT exhaust gas temperature and its measured value.
All the values in the above items a) to e) will naturally coincide with each other.
The following is an outline of the procedure for conducting the thermal efficiency diagnosis of the combined cycle power generation plant.
(1) To input a measuring data (PID) of a power generation plant to a computer.
(2) To perform calculation of optimum state estimation by taking a data accuracy into consideration so as to determine the heat balance.
(3) To compare the heat balance based on a design with the current heat balance.
(4) To analyze a degree of contribution of each equipment performance to the thermal efficiency.
(5) To specify the thermal efficiency deterioration causative equipment.
Taking the objects and the above matters into consideration, the present invention provides, in one aspect, a thermal efficiency diagnostic method of a combined power generation plant, comprising the steps of:
using measurement values of parameters relative to an energy input and an output with regard to respective equipments of a combined power generation plant including a gas turbine facility and a steam turbine facility, etc., and recording a design value of each equipment;
using measurement data having high accuracy as standard parameter, which is rigid through optimum state estimation of a heat balance;
using measurement data, which affect diagnostic results to a large degree and which are difficult to be measured with high accuracy, as key parameters;
using a number of calculation data of the heat balance as reference parameters, which are compared with their reference values in order to calculate the entire probability of the heat balance;
conducting optimum state estimation of the heat balance by adjusting the key parameters so as to be consistent with the standard parameters and so that each deviation of reference parameters becomes minimum as a whole and the probability becomes maximum in the plant;
comparing the heat balance thus determined with the heat balance based on a design value;
analyzing degree of contribution of performance of each respective equipment to thermal efficiency; and
specifying an equipment which causes heat efficiency deterioration in accordance with the degree of contribution.
In preferred examples of this aspect, the parameters of the energy input and the energy output include at least one item of temperature, pressure, flow rate and electric power output.
A generator power output is used as the standard parameter having high measurement accuracy, and a gas turbine exhaust gas flow rate and a gas turbine exhaust gas temperature are used as the key parameters which affect the diagnostic results to a large degree and which are difficult to be measured with high accuracy and to be adjusted through optimum state estimation.
A deviation of HRSG efficiency between the different calculation methods, an ST efficiency between the calculation value and the design value, a GT efficiency between the calculation value and the design value, a turbine power output between the measurement value by a torque sensor and the calculation value, etc. are used as reference parameters to calculate the probability of the heat balance.
In this aspect, the parameters of the energy production and the energy consumption includes at least one of temperature, pressure, flow rate and electric power output. A generator power output is used as a measuring value of the equipment having a high measuring accuracy. A gas turbine exhaust gas flow rate and a gas turbine exhaust gas temperature are used as a measuring value of an equipment which is a key parameter of the diagnosis and which is hard to be measured with high accuracy.
In another aspect of the present invention, there is also provided a thermal efficiency diagnostic apparatus of a combined power generation plant, comprising:
a sensor for measuring heat input and output of respective equipments constituting a combined power generation plant including a gas turbine facility and a steam turbine facility;
a memory for storing measurement data output from the sensor together with a design value and a calculation value of parameters related to a heat balance;
a heat balance calculating element for accurately calculating energy input and output of individual equipment in the entire plant;
an optimum state estimation element for calculating an optimum heat balance by using accurate measurement values as standard parameters, which are always rigid, and adjusting key parameters, which largely influence result of diagnosis and are difficult to be obtained with high accuracy, so that a deviation of reference parameters becomes minimum in the entire plant and the probability that of the heat balance of the plant becomes maximum;
a comparing element for comparing the heat balance thus determined by the optimum state estimation element with the heat balance based on the design value; and
a specifying element for analyzing a degree of contribution of performance of each equipment to thermal efficiency and specifying the equipment which causes thermal efficiency deterioration on the basis of the degree of contribution.
As is evident from the above description of the preferred embodiment, according to the present invention, the optimum state evaluation is used to specify the portion or equipment to which the deterioration is caused, thus improving an accuracy of the heat efficiency diagnosis in a combined power generation plant. Furthermore, it is possible to effectively perform the heat efficiency diagnosis and to accurately analyze an influence of the performance change of each of the equipments and the like to whole the power plant. Furthermore, it is also possible to more properly recover a heat efficiency through the periodic inspection, repair and the like and to obtain a great effect in economics.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.